CoRoT-7 b is the first confirmed rocky exoplanet , but , with an orbital semi-major axis of 0.0172 AU , its origins may be unlike any rocky planet in our solar system .
In this study , we consider the roles of tidal evolution and evaporative mass loss in CoRoT-7 b ’ s history , which together have modified the planet ’ s mass and orbit .
If CoRoT-7 b has always been a rocky body , evaporation may have driven off almost half its original mass , but the mass loss may depend sensitively on the extent of tidal decay of its orbit .
As tides caused CoRoT-7 b ’ s orbit to decay , they brought the planet closer to its host star , thereby enhancing the mass loss rate .
Such a large mass loss also suggests the possibility that CoRoT-7 b began as a gas giant planet and had its original atmosphere completely evaporated .
In this case , we find that CoRoT-7 b ’ s original mass probably didn ’ t exceed 200 Earth masses ( about 2/3 of a Jupiter mass ) .
Tides raised on the host star by the planet may have significantly reduced the orbital semi-major axis , perhaps causing the planet to migrate through mean-motion resonances with the other planet in the system , CoRoT-7 c. The coupling between tidal evolution and mass loss may be important not only for CoRoT-7 b but also for other close-in exoplanets , and future studies of mass loss and orbital evolution may provide insight into the origin and fate of close-in planets , both rocky and gaseous .